Environmental pollution has occurred in the vicinity of certain plants for wood preservation with water solutions of preservatives containing metal salts through spillage of such solutions from apparatus and wood, with the result that the underlying soil has been contaminated. Some of these preservatives are based on compounds of copper, chromium and pentavalent arsenic. The two first substances are commonly fixed in the soil to such a degree that as a rule they have not been considered dangerous. However, the arsenic acid has not been fixed to the same degree, and furthermore it is not so resistant against acidity as copper and chromium, i.e., is more easily dissolved. The question has been raised whether further increased soil acidity could cause movement of the arsenic acid and a spreading to more sensitive regions.
The investigations carried out up to now do not indicate future problems. However, an increased acidity cannot be excluded--sometimes such a situation is considered plausible--and how far this will proceed in such a case and what consequences it will have cannot be foreseen.
Furthermore, popular concern over such potential hazards can influence public opinion and cause irritation. It is thus of importance to find a way to solve the problems. If a relatively high content of arsenic acid is present in a small amount of soil, a carrying away of the contaminated soil may be recommended. Even a leaching of the soil with strong acid can technically be carried out. The present invention does not cover these two possibilities which are of less interest.